In the art of papermaking, an aqueous suspension containing cellulosic fibres, and optional fillers and additives, referred to as stock, is fed through pumps, screens and cleaners, which subject the stock to high shear forces, into a headbox which ejects the stock onto a forming wire. Water is drained from the stock through the forming wire so that a wet web of paper is formed on the wire, and the web is further dewatered and dried in the drying section of the paper machine. Drainage and retention aids are conventionally introduced at different points in the flow of stock in order to facilitate drainage and increase adsorption of fine particles such as fine fibres, fillers and additives onto the cellulose fibres so that they are retained with the fibres on the wire. Examples of conventionally used drainage and retention aids include organic polymers, inorganic materials, and combinations thereof.
EP 0 234513 A1, WO 91/07543 A1, WO 95/33097 A1 and WO 01/34910 A1 disclose the use of cationic starch and an anionic polymer in paper-making processes. However, there is nothing disclosed about adding both these components to the suspension after all points of high shear.
It would be advantageous to be able to provide a papermaking process with further improvements in drainage, retention and formation.